


The Pact

by omegadeanlovesalphacas



Category: Supernatural
Genre: Alpha Castiel, Alpha forcibly changed into an omega, Alpha/Beta/Omega Dynamics, Alpha/Omega, Come Eating, Dominance, Dubious Consent, M/M, Mpreg, Omega Dean
Language: English
Status: Completed
Published: 2016-11-04
Updated: 2016-11-04
Packaged: 2018-08-29 00:00:39
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 1,638
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/8468023
Author URL: https://archiveofourown.org/users/omegadeanlovesalphacas/pseuds/omegadeanlovesalphacas
Summary: Dean is born an Alpha, but Cas is determined to change that





	

**Author's Note:**

> Warning! This is an Alpha/omega kink prompt fill. Expect more porn than plot, and lots of power imbalance between Cas and Dean. Mind the warnings and kinks in the tags.
> 
> Anonymous asked:  
> I would love to read a fanfic where Cas would feed Dean his cum (can be secretly and it would eventually be explicitly) which would turn the alpha into an omega! Then, Dean has to learn his new place as alpha Cas' bitch and would get impregnated. I would love the end to have Dean as the new omega mommy of their ever growing family. :)
> 
> Filled on Tumblr, March 2015

Dean and Cas had been best friends since they were kids. When they were twelve they made a pact that if one of them was an Alpha and the other an omega, they would be mates. At fourteen Castiel presented as Alpha. Dean wasn’t exactly hoping to be an omega, but he didn’t break the pact. But when Dean also presented as an Alpha at fifteen, the pact was off. Cas could still remember Dean’s exact words, “I guess we’re just meant to be best friends, not mates.”

It wasn’t as if two Alphas _couldn’t_ mate, it was just frowned upon. Since neither of them could bare children, they’d have to take an omega to bear pups for them, and Castiel had no interest in bringing a third person between himself and Dean. What if Dean loved the omega more than him?

It wasn’t that Castiel didn’t want an omega, he just wanted _Dean_ to be his omega. He wanted Dean to submit to him and bear his pups, he’d dreamt about it for years, he wasn’t able to let go. 

The was one thing he could do. It may not work, it was said to only work for compatible mates. But Dean and Cas were compatible, Castiel was sure of it. It was said when two Alphas mated together, one Alpha could dominate the other, forcing it to biologically shift into an omega. But with a little research Castiel discovered it wasn’t triggered by the act of domination, it was triggered by the submitting Alpha taking in the seed of the dominant one, either from sucking a knot or being fucked by one. 

So Castiel started to form a plan. And when Dean turned eighteen and started to talk about looking for a mate, Cas decided it was time to put it into action. 

It would be easy. The two of them had just graduated high school and moved into a small apartment near the college they would be attending in the fall. From the moment they moved in, Castiel started doing all the cooking. Dean loved Castiel’s food, so he didn’t question it. And he didn’t notice when Cas started to slip his own seed into each of Dean’s meals, morning, noon and night. 

It took all summer, and there were a few near misses where Dean nearly stumbled on the truth, but by August Castiel started to see the changes. Dean’s frame was slowly getting smaller, he was losing the bulk of his muscle mass. His personality was getting softer, and he was starting to defer to Castiel’s choices, letting Cas tell him what to do, asking for suggestions for what he should wear. Little things that all started to add up to an omega personality. 

But it all came to a head one day, when Dean came barreling out of his bedroom, red in the face. Castiel was sitting on the couch, reading a book, and he looked up at Dean, who was clearly freaking out. 

“My knot is gone!” Dean yelled, arms waving, feet pacing. “I knew something has been weird for a while, I’ve felt kinda off, but now I can’t even produce a damn knot! I think I’m dying, I need to go see a doctor!”

“Dean, come here,” Castiel ordered smoothly. He pointed to the carpet between his knees. “Kneel.”

The command snapped Dean out of his panic, and he did as he was told, kneeling at Castiel’s feet. He frowned in confusion when his actions caught up to him. “Why did I do that? What’s wrong with me?”

“Nothing is wrong with you,” Castiel said, petting Dean’s face softly. “I’ve had my suspicions for a while, but I think I know what’s happening.”

Dean frowned, but couldn’t help melting into Castiel’s touch. “What, Cas?”

“You’re shifting,” Castiel said, running a thumb across Dean’s bottom lip. “It happens sometimes between mated Alphas, and I think living with me is making it happen to you.” Castiel was lying, but he knew he couldn’t admit the truth, not if he wanted Dean to stay with him.  “You’re becoming an omega, Dean.”

“What?” Dean yelped, pulling back. “That’s impossible!” 

Castiel just smirked and grabbed Dean’s face with both hands, pulling him in for a deep kiss. He pressed his tongue past Dean’s lips, exploring and claiming the now omega’s mouth. 

Dean whimpered into the kiss, shocked to feel his whole body submit to the Alpha’s dominating tongue. He moaned when he felt need spark low in his belly, and he felt something wet leak from his hole. 

Slick. 

Suddenly Castiel was out of his seat and pushing Dean to the floor. The omega’s back hit the carpet and he stared up at his friend in shock, the Alpha was crawling over him, pupils blown wide with lust. 

“Submit to me, Dean,” Castiel growled, grabbing Dean’s cock through his jeans in a tight grip. “Tell me you’re my bitch.”

Dean gasped, a little afraid, but still desperate for more. But he resisted, not able to admit to himself what was happening. 

“I-I can’t, Cas,” Dean gasped, hips thrusting up into Castiel’s hand. “I’m an Alpha!”

“Not anymore,” Castiel snarled. He grabbed Dean and easily flipped him onto his belly. He used one firm hand on the back of Dean’s neck to pin his face to the floor, while the other pulled Dean’s ass up in the air, putting him into a proper submission position. “You’re an omega now, and I’m going to make you mine.”

Dean let out a long moan, mind going fuzzy at the pleasure flooding him, his body reacting to the domination. It was the final trigger needed for his shift to be complete, and he could feel the slick drenching the back of his jeans in response. 

“Submit to me, Dean,” Castiel repeated, voice firm and in control. “Tell me you’re my bitch.”

This time Dean didn’t hesitate, too far gone to fight it. “I submit, Alpha!” he gasped, thrusting his ass up towards Castiel. “I’m your bitch!”

Castiel grinned, reaching around to unbutton Dean’s jeans before yanking them down to his thighs, finally bearing the omega’s wet hole. Castiel plunged two fingers inside, making Dean yowl with pleasure as the Alpha quickly prepped him. 

Castiel only had the patience for minimal prep, and after a minute he pulled his fingers free, lining up his hard cock and thrusting into the omega’s wet channel. He let out a satisfied groan as he sunk in deep.

Dean keened at the mix of pleasure and pain as his Alpha filled him, cock thrusting deep and setting a steady rhythm. He wasn’t doubting anything now, all he knew was this was right, this was everything he wanted. He whimpered and moaned as he felt Castiel’s knot start to swell, stretching him wider and pressing against his prostate with each thrust, sending little bolts of pleasure racing through him. 

Castiel’s thrusts got faster and harder, hips slapping against Dean’s ass as he pumped into him. He wanted Dean to feel this for a week, wanted him to _know_  he was owned. As he got close he switched her sharp little thrusts, his knot putting more and more pressure on Dean’s sweet spot. Castiel grabbed the back of Dean’s neck and growled. “Come on my knot, little bitch.”

Dean came on command, orgasm surprising him as it was ripped from his body, and he let out a long howl of pleasure before slumping into the carpet. 

Castiel growled and leaned down to bite hard on the back of Dean’s neck, finally claiming the omega he’d always wanted. His teeth held tight as his knot slammed into place, his own orgasm crashing over him, knot tied and pumping Dean full of his seed. 

Castiel growled into the back of Dean’s neck as he caught his breath, finally letting go after a few minutes. He easily lifted Dean in his arms, and his new mate gasped when he brought him down on his lap on the couch, pushing his knot deeper into his channel. 

“Are you okay?” Castiel asked, his brain finally catching up with what had just happened. 

Dean laughed, leaning back into Castiel’s chest. “I’m so much more than okay,” he said. “That was fucking amazing.” He turned his head to look up at Cas, grinning at him. “I guess this means the pact is back on.”

Castiel just smiled and kissed his new mate.

* * *

 

18 months later, and Castiel still couldn’t believe his plan worked. He was glad to have his parents’ trust fund, letting Castiel continue with school and support his family at the same time. Castiel had been surprised when Dean had asked his permission to drop out of school, telling Cas he just wanted to focus on being a good mate and house omega. Castiel had been secretly thrilled, the possessive Alpha loved keeping his omega safely at home. 

Castiel was just coming home from class, and he let himself into his and Dean’s little flat. “Hello Dean, I’m home!” he called out. 

“In the kitchen, Alpha!” Dean called back. 

Now that they were mated, Dean was learning how to do the cooking, he said he liked taking care of his Alpha. Castiel rounded the corner to the kitchen, smiling at the sight that greeted him.

Dean was dressed only in a pair of jeans, slung low on his hips. He was moving a bit slower these days, slowed down by his very pregnant belly and the nine month old pup on his hip. The omega grinned when he saw his mate, happy to melt into Castiel’s arms. “Missed you, Alpha,” he said, pressing his face to Castiel’s chest.

“Missed you too, omega,” Castiel said, kissing the top of his pup’s head before pulling Dean’s face up for a proper kiss. 

**Author's Note:**

> Thanks for reading! Comments are love! <3
> 
> Visit me on Tumblr: [omegadeanlovesalphacas.tumblr.com/mobilemenu.](http://omegadeanlovesalphacas.tumblr.com/mobilemenu)


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